Method and a system for communicating information to a land surveying rover located in an area without cellular coverage

ABSTRACT

Embodiments of the present invention pertain to methods and systems for communicating information to a roving positioning device. In one embodiment, a cellular communication device, a non-cellular wireless communication device, and a computer networking device for forwarding data packets are coupled with a bus. A request originating from a roving positioning device for a location-specific position correction is received via the non-cellular wireless communication device. A controller coupled with the bus causes the request to be forwarded via the cellular communication device.

RELATED APPLICATIONS

The present invention benefits from U.S.P.T.O. application No.10/666,079 filed Sep. 19, 2003 titled “A Method and System forDelivering Virtual Reference Station Data,” by Brent O'Meagher, assignedto the assignee of the present invention, and which is herebyincorporated by reference in it entirety herein.

TECHNICAL FIELD

Embodiments of the present invention relate to land surveying. Morespecifically, embodiments of the present invention relate to providingcommunications to apparatuses located in areas that do not have cellularcoverage.

BACKGROUND ART

Land surveying companies and earth moving companies use rovers that canmove around to survey areas of land or to move earth for variousreasons. Rovers can be associated with many types of earth-movingmachinery such as bulldozers, graders, and the like. In order to performthe Real Time Kinematic survey process, the rovers must receive datafrom at least one GNSS/GPS reference station, usually via a radio link.Modern methods now make use of a plurality of such reference stations,whose data is brought together for further processing at a particularprocessing center, or Network corrections control center. The roverscommunicate with a control center to obtain correction data derived fromthe plurality of reference stations, as described in U.S. Pat. No.5,477,458, hereby incorporated by reference in its entirety herein. Thenetworked corrections process has evolved to the point where theaccuracy available at a rover is now similar to what is obtained at asingle GNSS/GPS reference station. Hence the term “Virtual ReferenceStation” has come to apply to a rover receiver operating with networkedcorrections from a plurality of GNSS/GPS reference stations.

Networked corrections may be delivered to a particular rover via acellular connection, or, if sufficiently close to a control center, viaradio broadcasting method. However, cellular communication is notavailable in many parts of the world, particularly where infrastructuredevelopment is underway, as in many construction projects which requiresurveying or earthmoving activities, and traditional radio broadcastingmethods have limited range. Thus there is a need for an improvedcommunications path from rover to a networked corrections controlcenter.

DISCLOSURE OF THE INVENTION

Embodiments of the present invention pertain to methods and systems forcommunicating information to a roving positioning device located in anarea without cellular coverage. In one embodiment, a cellularcommunication device, a non-cellular wireless communication device, anda computer networking device for forwarding data packets are coupledwith a bus. A request originating from a roving positioning device for alocation-specific position correction is received via the non-cellularwireless communication device. A controller coupled with the bus causesthe request to be forwarded via the cellular communication device.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention. The drawings referred to in this description should not beunderstood as being drawn to scale except if specifically noted.

FIG. 1 is a block diagram of a router for communicating information to aland surveying rover located in an area without cellular coverage,according to one embodiment of the present invention.

FIG. 2 is a block diagram of a router for communicating information to aland surveying rover located in an area without cellular coverage,according to another embodiment of the present invention.

FIG. 3 is a block diagram of a system with a rover that a router isassociated with for communicating information to other rovers that arelocated in an area without cellular coverage, according to oneembodiment of the present invention.

FIG. 4 is a flowchart of a method for establishing communication betweena rover and a control center in accordance with embodiments of thepresent invention.

FIG. 5 is a flowchart of a method for requesting network-derivedcorrections from a mobile GNSS/GPS receiver in accordance withembodiments of the present invention.

FIG. 6 is a flowchart of a communications access command sequence inaccordance with embodiments of the present invention.

FIG. 7 is a flowchart of a method for delivering GNSS/GPS correctiondata from a source of GNSS/GPS correction data in accordance withembodiments of the present invention.

FIG. 8 is a flowchart of a method requesting GNSS/GPS correction datafor use by a mobile GNSS/GPS receiver in accordance with embodiments ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to various embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims. Furthermore, in the following description of thepresent invention, numerous specific details are set forth in order toprovide a thorough understanding of the present invention. In otherinstances, well-known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

Communications System in Accordance with Embodiments of the PresentInvention

FIG. 1 is a block diagram of an exemplary system 100 for communicatinginformation to a land surveying rover located in an area withoutcellular coverage, according to embodiments of the present invention. Itis noted that the blocks in FIG. 1 can be arranged differently than asillustrated, and can implement additional or fewer features than whatare described herein. Further, the features represented by the blocks inFIG. 1 can be combined in various ways. It is noted that in embodimentsof the present invention, system 100 may be a rover. A rover is mobiledevice and typically has a GPS receiver, or another type of positiondetermining system. Rovers are typically used by land surveying andearth moving companies. A rover can be a device that a human canphysically carry around as a surveying instrument. Alternatively, arover can be associated with heavy equipment such as a bulldozer or agrader.

As depicted in FIG. 1, the system 100 includes a cellular communicationdevice 110 and a non-cellular communications device 120 which arecommunicatively coupled via a bus 101. The cellular communicationsdevice 110 can use Internet protocols, such as Transmission ControlProtocol/Internet Protocol (TCPIP), packet switching, Institute ofElectronic and Electronics Engineers (IEEE) 802.11 standard, WirelessLocal Area Network (Wi Lan), IEEE 802.16 standard (also commonly knownas “WiMax”), and general packet radio service (GPRS), among otherthings. The cellular communications device 110 can use standards-basedmobile internet protocols (IP) to provide interoperability betweennetworks, while allowing for future network expansions and upgrades.Cellular communications device 110 may be used to communicate with a RTKcontrol center in embodiments of the present invention.

In embodiments of the present invention, the non-cellular communicationsdevice 120 is a two-way radio. Non-cellular communication device 120 canuse spread spectrum, ultra high frequency (UHF), 450 megahertz, 35megahertz, 900 megahertz, 2.4 gigahertz (GHz), and 5.8 gigahertz, radiofrequencies. Non-cellular communications device 120 typically uses apart of the radio spectrum that is allocated by the FCC on an unlicensedbasis, such as 900 megahertz, 2.4 GHz, or 5.8 GHz, but is not limited tounlicensed radio frequencies alone. According to a preferred embodiment,non-cellular communication device 120 uses 2.4 gigahertz. Furthernon-cellular communications device 120 can use time division multipleaccess (TDMA) broadcast methods well known in the arts.

Typically, cellular communications devices can communicate furtherdistances and at higher baud rates than non-cellular communicationsdevices. However, a non-cellular communication device is more rugged andless expensive than cellular communications device. Further,non-cellular communications device can be used practically any where inthe world while cellular communications devices are limited by theircoverage areas. By using cellular communications between a first roverand the control center, and non-cellular communications between thefirst rover and other rovers, the rovers without cellular coverage andthe control center can communicate far distances. Further, money can besaved by associating non-cellular communications devices with most ofthe rovers, or by only using one cellular communication device toforward position requests and corrections.

In the embodiment of FIG. 1, system 100 further comprises a router 130which is coupled with bus 101. In embodiments of the present invention,router 130 is for establishing data communications with other roverswithin range of one another using non-cellular communications device120. As will be explained in greater detail below, router 130 permits arover to receive GPS position data from a control center, even when therover is outside of a cellular communications network coverage area. Inembodiments of the present invention, router may be implemented withsoftware, firmware, hardware, or with a combination thereof.

Typically, each rover has a unique identifier, such as an Internetprotocol (IP) address. The unique identifier can be stored in memory(e.g., 140 of FIG. 1) associated with the rover, or in an internalmemory of router 130. The rovers can use these unique identifiers toidentify each other for the purposes of communicating. Normal IPaddressing schemes can be used for communicating between the rovers andbetween a router and a control center. An example of using wirelessInternet to distribute GPS information in accordance with embodiments ofthe present invention is described in U.S. Pat. No. 6,324,473, entitled“Method and Apparatus for Collecting, Processing, and DistributingDifferential Global Positioning System Information Using the Internet,”by Ralph Eschenbach, assigned to the assignee of the present inventionand incorporated as reference herein in its entirety.

As will be described in greater detail below, system 100 may be used inconjunction with rovers which are not equipped with cellularcommunications devices. For example, system 100 may be emplaced in anarea having cellular coverage and be used to forward messages to thecontrol center from a rover that does not have a cellular connection.

Memory 140 is for storing data and instructions for system 100. In oneembodiment, memory 140 may comprise a volatile memory such as RAM. It isnoted that system 100 may comprise other data storage devices which arenot shown in FIG. 1 for clarity. For example, system 100 may alsocomprise non-volatile memory (e.g., flash memory or ROM), a datadisplay, removable data storage, or a combination thereof.

In the embodiment of FIG. 1, system 100 further comprises a controller150. Controller 150 is for processing information and instructions.Additionally, controller 150 is for coordinating communications forsystem 100 using either or both of cellular communication device 110 andnon-cellular communication device 120.

In the embodiment of FIG. 1, system 100 further comprises a datacollector 160. Data collector 160, according to one embodiment, is acomputer system, such as a personal data assistant (PDA), that can beused to enter data into the system 100 or to process the data, or acombination thereof. For example, the data collector 160 can receive andstore a description of what system 100 is being used for, such as aspecific location or a construction site. In another example, the datacollector 160 can be used to receive and store a unique identifier ofthe system 100.

In the embodiment of FIG. 1, system 100 further comprises a positiondetermining system 170 which is coupled with bus 101. Positiondetermining system 170 determines the geographic position of a rover(e.g., system 100). For the purposes of the present invention, the term“geographic position” means the determining in at least two dimensions(e.g., latitude and longitude), the location of system 100. In oneembodiment of the present invention, position determining system 170 isa satellite based position determining system and receives navigationdata from satellites via an antenna (not shown). Examples of satellitebased position determining systems include the global positioning system(GPS) navigation system, a differential GPS system, a real-timekinematics (RTK) system, a networked RTK system, etc. While the presentembodiment recites these position determining systems specifically, itis appreciated that embodiments of the present invention are well suitedfor using other position determining systems as well such asground-based position determining systems, or other satellite-basedposition determining systems such as the Global Navigation SatelliteSystem (GNSS), the Global Orbiting Navigation Satellite System(GLONASS), or the Galileo system currently under development.

According to one embodiment, a flexible, compact form factor may usedfor system 100 which may include a rugged enclosure 180. The ruggedenclosure is designed so that the system can withstand harshenvironments due to high temperature variations, high altitude, shocks,vibrations, and exposure to damp or dusty environments. Further therugged enclosure enables the system 100 to be used in a moving vehicle.Instead of using an internal fan, the system 100 may utilize aconductive cooling system in the sealed enclosure 180.

FIG. 2 is a block diagram of an exemplary system 100 for communicatinginformation to a land surveying rover located in an area withoutcellular coverage, according to embodiments of the present invention. Inthe embodiment of FIG. 2, system 200 comprises a cellular communicationsdevice 210, a non-cellular communications device 220, a memory 240, acontroller 250, a data collector 260, and a position determining system270 which are communicatively coupled via a bus 201 and which aresimilar to the devices described above with reference to FIG. 1. In theembodiment of FIG. 2, the router (e.g., router 130 of FIG. 1) has beenreplaced with a bridge 230. In embodiments of the present invention, arouter may not be necessary if all of the routers which arecommunicating with system 200 all have the same subnet mask. Forexample, a bridge with a “cut-through” feature allows for fastforwarding of received packets in 64 bit sections without the errorchecking or control steps typically implemented by a router. As aresult, data throughput by bridge 230 may be appreciable faster than ifrouter 130 is used.

Overview of Position Determining Systems Used in Embodiments of thePresent Invention

Differential GPS

Differential GPS (DGPS) utilizes a reference station which is located ata surveyed position to gather data and deduce corrections for thevarious error contributions which reduce the precision of determining aposition fix. For example, as the GPS signals pass through theionosphere and troposphere, propagation delays may occur. Other factorswhich may reduce the precision of determining a position fix may includesatellite clock errors, GPS receiver clock errors, and satelliteposition errors (ephemeredes). The reference station receivesessentially the same GPS signals as rovers which may also be operatingin the area. However, instead of using the timing signals from the GPSsatellites to calculate its position, it uses its known position tocalculate timing. In other words, the reference station determines whatthe timing signals from the GPS satellites should be in order tocalculate the position at which the reference station is known to be.The difference between the received GPS signals and what they optimallyshould be is used as an error correction factor for other GPS receiversin the area. Typically, the reference station broadcasts the errorcorrection to, for example, a rover which uses this data to determineits position more precisely. Alternatively, the error corrections may bestored for later retrieval and correction via post-processingtechniques.

Real Time Kinematic System

An improvement to DGPS methods is referred to as Real-time Kinematic(RTK). As in the DGPS method, the RTK method, utilizes a referencestation located at determined or surveyed point. The reference stationcollects data from the same set of satellites in view by the rovers inthe area. Measurements of GPS signal errors taken at the referencestation (e.g., dual-frequency code and carrier phase signal errors) andbroadcast to one or more rovers working in the area. The rover(s)combine the reference station data with locally collected positionmeasurements to estimate local carrier-phase ambiguities, thus allowinga more precise determination of the rovers position. The RTK method isdifferent from DGPS methods in that the vector from a reference stationto a rover is determined (e.g., using the double differences method). InDGPS methods, reference stations are used to calculate the changesneeded in each pseudorange for a given satellite in view of thereference station, and the rover, to correct for the various errorcontributions. Thus, DGPS systems broadcast pseudorange correctionnumbers second-by-second for each satellite in view, or store the datafor later retrieval as described above.

RTK allows surveyors to determine a true surveyed data point in realtime, while taking the data. However, the range of useful correctionswith a single reference station is typically limited to about 70 kmbecause the variable in propagation delay (increase in apparent pathlength from satellite to rover receiver, or pseudo range) changessignificantly for separation distances beyond 70 km. This is because theionosphere is typically not homogeneous in its density of electrons, andbecause the electron density may change based on, for example, the sun'sposition and therefore time of day. Thus for surveying or otherpositioning systems which must work over larger regions, the surveyormust either place additional base stations in the regions of interest,or move his base stations from place to place. This range limitation hasled to the development of more complex enhancements that have supercededthe normal RTK operations described above, and in some cases eliminatedthe need for a base station GPS receiver altogether. This enhancement isreferred to as the “Network RTK” or “Virtual Reference Station” (VRS)system and method.

Network RTK

Network RTK typically uses three or more GPS reference stations tocollect GPS data and extract information about the atmospheric andsatellite ephemeris errors affecting signals within the network coverageregion. Data from all the various reference stations is transmitted to acentral processing facility, or control center for Network RTK. Suitablesoftware at the control center processes the reference station data toinfer how atmospheric and/or satellite ephemeris errors vary over theregion covered by the network. The control center computer processorthen applies a process which interpolates the atmospheric and/orsatellite ephemeris errors at any given point within the networkcoverage area and generates a pseudo range correction comprising theactual pseudo ranges that can be used to create a virtual referencestation. The control center then performs a series of calculations andcreates a set of correction models that provide the rover with the meansto estimate the ionospheric path delay from each satellite in view fromthe rover, and to take account other error contributions for those samesatellites at the current instant in time for the rover's location.

The rover is configured to couple a data-capable cellular telephone toits internal signal processing system. The surveyor operating the roverdetermines that he needs to activate the VRS process and initiates acall to the control center to make a connection with the processingcomputer. The rover sends its approximate position, based on raw GPSdata from the satellites in view without any corrections, to the controlcenter. Typically, this approximate position is accurate toapproximately 4-7 meters. The surveyor then requests a set of “modelledobservables” for the specific location of the rover. The control centerperforms a series of calculations and creates a set of correction modelsthat provide the rover with the means to estimate the ionospheric pathdelay from each satellite in view from the rover, and to take intoaccount other error contributions for those same satellites at thecurrent instant in time for the rover's location. In other words, thecorrections for a specific rover at a specific location are determinedon command by the central processor at the control center and acorrected data stream is sent from the control center to the rover.Alternatively, the control center may instead send atmospheric andephemeris corrections to the rover which then uses that information todetermine its position more precisely.

These corrections are now sufficiently precise that the high performanceposition accuracy standard of 2-3 cm may be determined, in real time,for any arbitrary rover position. Thus the GPS rover's raw GPS data fixcan be corrected to a degree that makes it behave as if it were asurveyed reference location; hence the terminology “virtual referencestation.” An example of a network RTK system in accordance withembodiments of the present invention is described in U.S. Pat. No.5,899,957, entitled “Carrier Phase Differential GPS CorrectionsNetwork,” by Peter Loomis, assigned to the assignee of the presentinvention and incorporated as reference herein in its entirety.

The Virtual Reference Station method extends the allowable distance fromany reference station to the rovers. Reference stations may now belocated hundreds of miles apart, and corrections can be generated forany point within an area surrounded by reference stations. However,there are many construction projects where cellular coverage is notavailable over the entire physical area under construction and survey.

System for Communicating Information to a Land Surveying Rover Locatedin a Area Without Cellular Coverage

FIG. 3 depicts a block diagram of a system 300 for communicatinginformation to rovers that are located in an area without cellularcoverage in accordance with embodiments of the present invention. It isnoted that the blocks in FIG. 3 can be arranged differently than asillustrated, and can implement additional or fewer features than whatare described herein. Further, the features represented by the blocks inFIG. 3 can be combined in various ways.

As depicted in FIG. 3, system 300 comprises a control center 360 whichis communicatively coupled with three reference stations 330A, 330B,330C. A first rover (e.g., system 100 or system 200) comprising router130 is located in an area 340A that has cellular communications andtherefore can use cellular communication connection 352 to communicatewith the control center 360 via a cellular base station 390. Rovers 2-Nare located respectively in areas 340B-340N that do not provide cellularcommunications and are equipped with routers 130B and 130N as describedabove with reference to FIG. 1. Rovers 1-N can use their respectivenon-cellular communications devices to communicate with each other asdepicted by non-cellular communication connections 354 and 356.Furthermore, rover 2 and rover N may communicate via non-cellularcommunication connection 358. The GPS antennas of reference stations330A, 330B, and 330C can communicate with GPS/GNS satellites (notshown). Since the locations of the satellites are known in relation tothe reference stations 330A, 330B, 330C, the delay path of a GPS signalpassing through the ionosphere and troposphere at each of theselocations can be determined. The control center 360 can analyze thisinformation and use this information to generate a correction model(also referred to herein as “location specific position correction”)based upon the location information that a rover provided to the controlcenter 360.

In embodiments of the present invention, if a rover (e.g., rover 2)determines that it does not have a cellular communication capability, itcan make a data connection, using its respective non-cellularcommunications device 120, with a cellular enabled rover (e.g., rover1). Rover 2 may not have cellular capability due to, for example, beingoutside of a cellular coverage area, or because its respective cellularcommunication device 110 is not enabled. Thus, if rover 2 determinesthat it cannot communicate with control center 360 using cellularcommunication device 110, router 130B of rover 2 may be configured toattempt to make a data connection with router 130 of rover 1 whose IPaddress is pre-configured in the memory of router 130B. Router 130Bestablishes contact with router 130 and indicates that it is trying toestablish a connection with control center 360 via cellular connection352. The approximate location of rover 2 is forwarded via the dataprotocol of routers 130 and 130B and is then forwarded to the controlcenter 360. This is typically done via normal IP addressing schemeswherein the router 130 receives data packets from router 130B which aredestined for the control center 3601.

Control center 360 activates its internal process for determininglocation-specific “modelled observables” which are appropriate for theapproximate location sent by rover 2 as described above. The modelledobservables are sent back to rover 1 via cellular connection 352. Router130 of rover 1 checks the destination address for the data, determinesthat it is destined for router 130B of rover 2, and forwards the datavia non-cellular connection 354. Typically, the data is broadcast intothe ether, whereupon it is received by all comparably equippedrover/routers in the general vicinity, but is accepted only by rover 2due to its unique IP address.

In another embodiment, if rover N does not have a direct non-cellularcommunication connection with rover 1 (e.g., non-cellular communicationconnection 356 does not exist due to terrain masking of the signal), itcan forward its approximate location and request for a positioncorrection to rover 1 via rover 2. In a similar manner to that describedabove, router 130N of rover N may have the IP address of router 130B,and router 130 of rover 1, stored in its memory and will communicatedwith rover 2 via non-cellular communication connection 358 in order tosend and receive data to/from control center 360. Upon receiving thedata from rover N, rover 2 will attempt to communicate with controlcenter 360 as described above. When the modelled observables arebroadcast by rover 1, router 1 130B will examine the destination IPaddress of the data packets and automatically forward them to router130N by re-broadcasting the data. It is noted that while the examplesabove specifically teach the use of a router in rover 1, rover 2, androver N, embodiments of the present invention may utilize a bridge in asimilar capacity. For example, if rover 2 and rover N are in the samesub-network, the use of bridges may be appropriate. However, if rover 2and rover N are configured to operate in separate networks, the use of arouter is preferred.

Coordinating Information from Rovers

According to one embodiment, the information that the rovers 1-N provideto control center 360 may be coordinated. For example, the controlcenter 360 can correct the location information that the rovers 1-Nprovided using various models that are well known in the art and storethe corrected location information in a database. Since a lot ofinformation from a plurality of rovers is available, better surveyingcapabilities can be provided.

More specifically, rover 2 may be equipped with a geodata qualityantenna. The rover can remain stationary for approximately 180 secondswhile gathering information. The rover 2 can indicate to the controlcenter 360 when it is sitting still, or when it is moving. Rover 1 cancommunicate the gathered information to the control center 360 usingcellular communications device 110. In this case, the control center 360can provide better ionospheric and tropospheric modeling by accessingmore information from a plurality of rovers.

Construction Site Management

Earth moving equipment such as bulldozers and graders are used toprepare a site for construction. In the conventional art, a constructionsite may have stacks in the ground that indicate how deep the earthmovers are to cut. The earth movers have GPS receivers that can receivepositioning information from satellites. The positioning information isused for creating a three dimensional (3D) design of what the finishedground is supposed to look like. The finished ground is commonlyreferred to as a “rough grade.” The earth movers use the positioninginformation to determine where the tip of the blade should be. Thepositioning information simplifies the job of an earth mover operator sothat the operator only has to go backwards, forwards, right and left,but does not have to position the blade. This is commonly referred to as“stackless grade control” because it enables the operator to gradewithout stacks.

Since bulldozers are expensive, it would not make economic sense to makeall of the earth movers rely on cellular communications devices whichare more prone to communications failures than radios. Additionally, thecost associated with multiple cellular devices operating from one sitecan be prohibitive, especially, if fewer cellular devices are capable ofhandling all of the data being sent. In the conventional art, the earthmoving equipment use radios to communicate. This only enables the earthmoving equipment to communicate approximately 30 kilometers. Accordingto one embodiment of the present invention, one of the earth movers isequipped with a rover (e.g., system 100 or 200) having a cellularcommunication connection with a control center. The earth mover with thecellular connection can thus communicate with the control station onbehalf of the other earth movers which may be outside of the cellularcoverage area, or may simply have their cellular communication devicesdisabled. The earth movers can communicate their locations to thecontrol center 360 via the router 130, according to embodimentsdescribed herein. The control center 360 can use the locations that theearth movers provided to generate virtual reference stations for theearth movers, as described herein. The control center 360 cancommunicate the position correction data to the earth movers through therouter 100, according to embodiments described herein.

According to another embodiment, the control center 360 can coordinatethe activities of the earth movers on a site. For example, the earthmovers can communicate various types of information about the work, suchas measurements, they are doing back to the control center 360. Theearth movers can use a common interface for communicating information tothe control center 360. Further, the control center 360 can use the samejob file for all of the earth movers. The control center 360 can usethis information to coordinate the activities of the earth movers. Forexample, the control center 360 can provide each of the earth moverswith information about other earth movers on the site.

FIG. 4 is a flowchart of a method 400 for establishing communicationbetween a rover and a control center in accordance with embodiments ofthe present invention. It is noted that, in one embodiment, method 400is performed by the controller (e.g., 150 of FIG. 1) of each rover in anetwork. It is further noted that while the following discussion isdirected to system 100 of FIG. 1, method 400 is also applicable tosystem 200 of FIG. 2.

In step 401 power is initiated for system 100 and method 400 proceeds tostep 405.

In step 405 of FIG. 4, an operation is performed to determine whether asystem fault error has been received. In embodiments of the presentinvention, device polling may be performed to determine if a systemerror condition exists with a component of system 100 or system 200. Inother embodiments, each component may independently generate a messageto controller 150 conveying that a system error has occurred. It isnoted that reception of a system fault error message may be received atany time in method 400 and cause an immediate suspension of method 400.In embodiments of the present invention, if no system fault errorcondition exists, method 400 proceeds to step 410.

In step 410 of FIG. 4, an operation is performed to determine whethervalid GPS information is being received. In embodiments of the presentinvention, a sensor integrity check may be automatically performed whenpower is initiated to ensure that the sensors are providing validinformation. For example, a GPS sensor (e.g., position determiningsystem 170) can be operating properly (e.g., no system fault), but canbe providing useless information when the system is under trees, orexperiencing bad position quality. It is noted that integrity checks forsensors other than position determining system may be performed at thistime. If the GPS system (e.g., position determining system 170 ofFIG. 1) is receiving valid information, method 400 proceeds to step 415.

In step 415 of FIG. 4, an operation is performed to determine whethersystem 100 is enabled with a cellular communication device. Inembodiments of the present invention, some of the rovers in a networkmay not be equipped with a cellular communication device (e.g., 110 ofFIG. 1) in order to reduce the cost of system comprising a plurality ofrovers. In another embodiment, system 100 may be equipped with acellular communication device, however, the device is disabled. This maybe advantageous in situations in which it is desired to reduce thenumber of cellular connections maintained by a network in order toreduce costs. If it is determined that system 100 does have an enabledcellular communication device, method 400 proceeds to step 420. If it isdetermined that system 100 does not have an enabled cellularcommunication device, method 400 proceeds to step 421.

In step 420 of FIG. 4, an operation is performed to determine whether acellular communication signal exists at the location of system 100. Asdescribed above, rovers are often used in construction sites or surveyareas that are outside of a cellular communication network's coveragearea. Thus, even if system 100 is configured with an enabled cellularcommunication device, it may not be able to communicate with a controlcenter in order to send and receive data. In embodiments of the presentinvention, if a cellular communication signal is detected by system 100,method 400 proceeds to step 425. If no cellular communication signal isdetected by system 100, method 400 proceeds to step 421.

In step 421 of FIG. 4, the rover without a cellular communicationconnection waits to receive a message that identifies which rover in thenetwork will act as a gateway to the control center for RTK. Uponreceiving this message, the IP address of the gateway is stored by therouter. Method 400 then proceeds to step 435.

In step 425 of FIG. 4, a cellular communication connection isestablished with the control center for RTK. As described above, acellular communication connection is typically used to communicatebetween a rover and a control center for RTK. This is advantageousbecause of the higher baud rate and distance that a cellularcommunications network provides. In the embodiment of FIG. 4, once acellular communication connection is established between system 100 anda control center (e.g., 360 of FIG. 3), method 400 proceeds to step 430.

In step 430, the IP address of system 100 is broadcast usingnon-cellular communication device 120. In so doing, system 100 informsother rovers in range of the broadcast that it has established acellular communication connection with control center 360 and will serveas a gateway to the control center for the network of rovers. Thisinformation is stored by the routers associated with each of the otherrovers in the network. In embodiments of the present invention, method400 then proceeds to step 435.

In step 435 of FIG. 4, GPS data is forwarded to a control center. In oneembodiment, the GPS data may be generated by system 100 itself. Inanother embodiment, system 100 simply forwards GPS data for other roversin the network which do not have a cellular connection with the controlcenter. Thus, if a rover in the network (e.g., rover 2 of FIG. 3) doesnot have a direct cellular connection with the control center, therouter 130B can determine which router (e.g., router 130 of system 100)in the network acts as a gateway to the control center and generate amessage to system 100 indicating that data from rover 2 should beforwarded to the control center. Upon receiving this message, system 100examines the data packets from rover 2, and forwards the data to thecontrol center using cellular communication device 110. In embodimentsof the present invention, method 400 then proceeds to step 440.

In step 440, a location-specific position correction from the controlcenter is received by system 100. In embodiments of the presentinvention, this may be data destined for system 100 itself, or may bedestined for another rover (e.g., rover 2) via system 100. If the datais destined for another rover, system 100 will forward the data usingnon-cellular communication device 120. In embodiments of the presentinvention, system 100 may have to re-format the data prior tobroadcasting to the other rovers in the vicinity. The data packets willhave the IP address of the receiving rover (e.g., rover 2) in thedestination header. In embodiments of the present invention, all of therovers which receive the broadcast data will examine the header of thedata packets to determine if they are the destination. If they are notthe destination, the rovers will either discard the data packets, orupon examining their own router tables, re-broadcast the data in orderto forward it to the appropriate destination. Alternatively, if thereceiving rover is the correct destination for the data, the rover willuse that data to more precisely determine its geographic position.

FIG. 5 is a flowchart of a method 500 for requesting network-derivedcorrections from a mobile GNSS/GPS receiver in accordance withembodiments of the present invention. In step 510 of FIG. 5, a GNSS/GPSreceiver having a first address is communicatively coupled with a firstport on a router. As shown in FIG. 1, position determining system 170 iscoupled with router 130 via bus 101.

In step 520 of FIG. 5, a wireless transceiver is communicatively coupledwith a second port on the router. Referring again to FIG. 1,non-cellular communication device 120 is also coupled with router 130via bus 101.

In step 530 of FIG. 5, a cellular communication device iscommunicatively coupled with a third port on the router. Referring againto FIG. 1, cellular communication device 110 is coupled with router 130via bus 101.

In step 540 of FIG. 5, a processor for executing a communication accesscommand sequence is communicatively coupled with the router. Referringagain to FIG. 1, controller 150 is coupled with router 130 via bus 101.In embodiments of the present invention, controller 150 is forimplementing a communication access command sequence for communicativelycoupling a mobile GNSS/GPS receiver (e.g., rover 1 and/or rover 2 ofFIG. 3 with a control center.

FIG. 6 is a flowchart of a communications access command sequence 600 inaccordance with embodiments of the present invention. In embodiments ofthe present invention, sequence 600 may be performed by controller 150as described above in step 540 of FIG. 5. In step 610 of FIG. 6, a testfor cellular network connectivity is performed. In embodiments of thepresent invention, the GNSS/GPS receiver (e.g., rover 2) will firstattempt to communicate with the control center for RTK (e.g., controlcenter 360) using a cellular network connection.

In step 620 of FIG. 6, dialing instructions are accessed for thecellular communication device to contact a source of location-specificcorrection data if a cellular connection exists. In embodiments of thepresent invention, the dialing instructions may be accessed bycontroller 150, non-cellular communication device 120, router 130, etc.Upon establishing a cellular connection with the control center, theapproximate location of the rover can be sent, along with a request forthe modelled observables applicable to that location.

In step 630 of FIG. 6, a data message is generated which is to be sentvia the wireless transceiver if cellular network connectivity does notexist. If a determination is made that cellular network connectivitydoes not exist between a source of a location-specific positioncorrection and a mobile GNSS/GPS receiver, a data message is generatedwhich will be sent via the wireless transceiver to a second mobileGNSS/GPS receiver which does have cellular network connectivity. Inembodiments of the present invention, a plurality of mobile GNSS/GPSreceivers may be used to relay the data message from the GNSS/GPSreceiver which generated the data message and the GNSS/GPS receiverwhich has cellular network connectivity. The GNSS/GPS receiver whichdoes have cellular network connectivity then forwards the data messageto the source of location-specific correction data and also relaysreplies from the source of location-specific correction data back to theGNSS/GPS receiver which originated the data message.

FIG. 7 is a flowchart of a method 700 for delivering GNSS/GPS correctiondata from a source of GNSS/GPS correction data in accordance withembodiments of the present invention. In step 710 of FIG. 7, a requestfor GNSS/GPS correction data is received from a mobile GNSS/GPSreceiver. In embodiments of the present invention, the request comprisesan IP address which identifies the mobile GNSS/GPS receiver and itsapproximate current location. As described above, in embodiments of thepresent invention, a rover (e.g., rover 1 of FIG. 3) which hasestablished a cellular communication connection with a control center(e.g., 360 of FIG. 3) may act as a gateway for other rovers (e.g.,rovers 2 and rover N of FIG. 3) which do not have a cellularcommunication connection with the control center. Thus, upon determiningthat it does not have a cellular connection with control center 360, thecontroller of rover 2 causes router 130B to send a request for alocation-specific position correction, as well as the IP address ofrover 2, to rover 1. The request further comprises information thatinforms rover 1 that the data is intended for control center 360.

In step 720 of FIG. 7, correction data is prepared from at least onereference source based on the approximate current location of the mobileGNSS/GPS receiver. Upon receiving the request, control center 360creates a set of correction models that will provide rover 2 with themeans to estimate ionospheric path delay, as well as other errorcontributions, from satellites at the current instant in time for thelocation at which rover 2 is situated.

In step 730 of FIG. 7, the correction data is sent in a data message tothe specific IP address provided in step 710. In embodiments of thepresent invention, the correction models created by control center 360generates a reply which it sends to rover 2 via the cellular networkconnection established with rover 1. Upon receiving the reply, rover 1examines the IP destination header data to determine which mobileGNSS/GPS receiver the correction model data is destined. Upondetermining that the correction model data is destined for rover 2,rover 1 broadcasts the correction model data using non-cellularcommunication device 120. In embodiments of the present invention, oneor more additional mobile GNSS/GPS receivers may be utilized to relaycommunications between rover 1 and rover 2.

FIG. 8 is a flowchart of a method 800 requesting GNSS/GPS correctiondata for use by a mobile GNSS/GPS receiver in accordance withembodiments of the present invention. In step 810 of FIG. 8, a requestmessage is created containing an approximate current location of amobile GNSS/GPS receiver. As described above, in embodiments of thepresent invention, in networked RTK systems, a mobile receiverdetermines its approximate location and generates a request for themodelled observables applicable for the approximate location at whichthe receiver is located. In embodiments of the present invention therequest further comprises an IP address which uniquely identifies thereceiver.

In step 820 of FIG. 8, the request message is forwarded to a firstrouter coupled with the mobile GNSS/GPS receiver and uniquely identifiedby an IP address. In embodiments of the present invention, the firstrouter uses one of communications device selected from a cellularcommunications device and a wireless transceiver to forward the requestmessage to a source of correction data. If a cellular network connectionexists between the mobile GNSS/GPS receiver and the control center, themobile GNSS/GPS receiver will send the request message using thecellular communications device. If a cellular network connection doesnot exist between the mobile GNSS/GPS receiver, the request message issent using the wireless transceiver. More specifically, the wirelesstransceiver is used to send the request message to a mobile GNSS/GPSreceiver which does have a cellular network connectivity with the sourceof correction data.

The preferred embodiment of the present invention, a method and systemfor communicating information to a roving positioning device, is thusdescribed. While the present invention has been described in particularembodiments, it should be appreciated that the present invention shouldnot be construed as limited by such embodiments, but rather construedaccording to the following claims.

1. A communications system for providing GNSS/GPS location-specificcorrection data to a plurality of mobile GNSS/GPS receivers, said systemcomprising: a first mobile GNSS/GPS receiver at a first locationconfigured to incorporate said GNSS/GPS location-specific correctiondata in determining a position fix from GNSS/GPS satellite signals; acellular communication device coupled with said first mobile GNSSreceiver for informing a correction data source of the first location ofsaid first mobile GNSS receiver and for receiving a set of said GNSS/GPSlocation-specific correction data for delivering said correction data tosaid first mobile GNSS/GPS receiver; a first wireless router coupledwith said cellular communication device for forwarding a second set ofGNSS/GPS location-specific correction data to a second wireless routercoupled to a second GNSS/GPS receiver at a second location, wherein saidsecond GNSS/GPS receiver requests second set of GNSS/GPSlocation-specific correction data via said first wireless router andsaid cellular communication device.
 2. The system of claim 1 whereinsaid first wireless router and said second wireless router are uniquelyidentified using respective Internet Protocol (IP) addresses.
 3. Thesystem of claim 1 wherein said set of said GNSS/GPS location-specificcorrection data and said second set of said GNSS/GPS location-specificcorrection data are derived from reference station data which areprocessed by said correction data source.
 4. The system of claim 1further comprising: a memory device coupled with said first wirelessrouter for storing a description of a communication pathway to saidsecond wireless router and to said correction data source.
 5. The systemof claim 1 wherein said cellular communication device is compliant witha standard selected from the group consisting essentially of astandards-based mobile internet protocol, packet switching, wirelesslocal area network, Institute of Electrical and Electronics Engineers(IEEE) 802.11 standard, IEEE 802.16 standard, and general packet radioservice (GPRS).
 6. The system of claim 1 wherein said first wirelessrouter and said second wireless router are compliant with a standardselected from the group consisting essentially of licensed radiocommunications, and unlicensed radio communications operating in thefrequency bands comprising 900 MHz, 5.8 GHz, and 2.4 GHz.
 7. The systemof claim 1 further comprising: a controller coupled with said cellularcommunication device and with said first wireless router, saidcontroller for causing a request originating from second GNSS/GPSreceiver for said second set of location-specific correction data to beforwarded via said cellular communication device.
 8. A method forrequesting network-derived corrections from a mobile GNSS/GPS receiver,said method comprising: communicatively coupling a mobile GNSS/GPSreceiver having a first IP address with a first port on a router;communicatively coupling a wireless transceiver with a second port onsaid router; communicatively coupling a cellular communication devicewith a third port on said router; communicatively coupling a processorwith said router said processor for executing a communications accesscommand sequence comprising; testing for a cellular networkconnectivity; accessing dialing instructions for said cellularcommunication device to contact a source of location-specific correctiondata if cellular network connectivity exists; and generating a datamessage to be sent via said wireless transceiver if said cellularnetwork connectivity does not exist, said data message comprising anInternet Protocol (IP) address of said router, an approximate currentlocation of said mobile GNSS/GPS receiver, and a request for correctiondata.
 9. The method as recited in claim 9 further comprising:automatically identifying a second mobile GNSS/GPS receiver which doeshave a cellular communication network connection with said source oflocation-specific correction data; and sending said data message to asecond router associated with said second mobile GNSS/GPS receiver. 10.The method as recited in claim 9 further comprising: said second mobileGNSS/GPS receiver automatically forwarding said data message to saidsource of location-specific correction data using said cellularcommunication network connection; generating a response to said datamessage by said source of location-specific correction data; and saidsecond mobile GNSS/GPS receiver receiving said response via saidcellular communication network connection.
 11. The method as recited inclaim 10 further comprising: said second mobile GNSS/GPS receiveridentifying said Internet Protocol (IP) address associated with saidwireless router; and said second mobile GNSS/GPS receiver forwardingsaid response to said router via said wireless transceiver.
 12. Themethod as recited in claim 10 wherein said generating a response furthercomprises: using reference station data to derive a set of correctiondata that is appropriate for said mobile GNSS/GPS receiver.
 13. Themethod as recited in claim 8 further comprising: using a cellularcommunication device which is compliant with a standard selected fromthe group consisting essentially of a standards-based mobile internetprotocol, packet switching, wireless local area network, Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard, IEEE 802.16standard, and general packet radio service (GPRS).
 14. The method asrecited in claim 8 further comprising: said wireless transceiver using acommunication pathway which is compliant with a standard selected fromthe group consisting essentially of licensed radio communications, andunlicensed radio communications operating in the frequency bandscomprising 900 MHz, 5.8 GHz, and 2.4 GHz.
 15. The method as recitedclaim 8 further comprising: determining said approximate currentlocation of said mobile GNSS/GPS receiver using a position determiningsystem which is selected from the group consisting essentially of theGlobal Positioning System, the Global Navigation Satellite Service, theGlobal Orbiting Navigation Satellite System, and the Galileo navigationsystem.
 16. A method for delivering GNSS/GPS correction data from asource of GNSS/GPS correction data, said method comprising: receiving arequest for said GNSS/GPS correction data from a mobile GNSS/GPSreceiver, said request conveying an Internet Protocol (IP) address whichidentifies a first router associated with said mobile GNSS/GPS receiverand an approximate current location of said mobile GNSS/GPS receiver;preparing correction data from at least one reference source based onsaid approximate current location of said mobile GNSS/GPS receiver; andsending said correction data in a data message to said specific IPaddress.
 17. The method as recited in claim 12 further comprising:accessing reference station data to derive said correction data that isappropriate for said mobile GNSS/GPS receiver.
 18. The method as recitedin claim 16 further comprising: receiving said request via a secondmobile GNSS/GPS receiver and wherein said request is conveyed via acellular communication network; sending said data message to said secondmobile GNSS/GPS receiver via said cellular communication network; andsaid second mobile GNSS/GPS receiver forwarding said data message tosaid GNSS/GPS receiver via a non-cellular wireless message.
 19. Themethod as recited in claim 18 further comprising: identifying said firstrouter associated with said mobile GNSS/GPS receiver using said IPaddress using a second router associated with said second mobileGNSS/GPS receiver.
 20. The method as recited in claim 19 furthercomprising: attempting to send said request via said cellularcommunication network; and said first router automatically generating asecond non-cellular wireless message which conveys said request and saidIP address in response to determining that said request cannot be sentvia said cellular communication network.
 21. The method as recited inclaim 18 further comprising: using a cellular communication networkwhich is compliant with a standard selected from the group consistingessentially of a standards-based mobile internet protocol, packetswitching, wireless local area network, Institute of Electrical andElectronics Engineers (IEEE) 802.11 standard, IEEE 802.16 standard, andgeneral packet radio service (GPRS).
 22. The method as recited in claim18 wherein said forwarding said data message further comprises: sendingsaid data message to said mobile GNSS/GPS receiver using a non-cellularwireless communication.
 23. The method as recited in claim 22 furthercomprising: using a non-cellular wireless communication which iscompliant with a standard selected from the group consisting essentiallyof licensed radio communications, and unlicensed radio communicationsoperating in the frequency bands comprising 900 MHz, 5.8 GHz, and 2.4GHz.
 24. The method as recited claim 16 further comprising: determiningsaid approximate current location of said mobile GNSS/GPS receiver usinga position determining system which is selected from the groupconsisting essentially of the Global Positioning System, the GlobalNavigation Satellite Service, the Global Orbiting Navigation SatelliteSystem, and the Galileo navigation system.
 25. A method for requestingGNSS/GPS correction data from a source of GNSS/GPS correction data foruse by a mobile GNSS/GPS receiver, said method comprising: creating arequest message containing an approximate current location of saidmobile GNSS/GPS receiver; and forwarding said request message to a firstrouter coupled with said mobile GNSS/GPS receiver and uniquelyidentified by an Internet Protocol (IP) address, and wherein said firstrouter uses one of a communications device selected from the groupcomprising: a cellular communication device, or a wireless transceiverto forward said request message to said source of correction data. 26.The method as recited in claim 25 further comprising: said first routerdetermining that communication with said source of GNSS/GPS correctiondata is not possible using said cellular communication device; and saidfirst router automatically using said wireless transceiver to conveysaid request message and said IP address in response to saiddetermining.
 27. The method as recited in claim 26 further comprising:accessing a routing table to identify a second router which iscommunicatively coupled with said source of GNSS/GPS correction data viaa cellular communication network; and forwarding said request message tosaid second router wherein said request message conveys said IP addressof said first router.
 28. The method as recited in claim 27 furthercomprising: using a cellular communication network which is compliantwith a standard selected from the group consisting essentially of astandards-based mobile internet protocol, packet switching, wirelesslocal area network, Institute of Electrical and Electronics Engineers(IEEE) 802.11 standard, IEEE 802.16 standard, and general packet radioservice (GPRS).
 29. The method as recited in claim 27 furthercomprising: said second router forwarding said request message to saidsource of GNSS/GPS correction data via said cellular communicationnetwork; and said second router receiving response from said source ofGNSS/GPS correction data via said cellular communication network, saidresponse comprising location-specific correction data which is derivedbased upon said approximate current location of said mobile GNSS/GPSreceiver.
 30. The method as recited in claim 29 further comprising: saidsecond router forwarding said response to said first router using saidwireless transceiver.
 31. The method as recited in claim 25 furthercomprising: using a wireless transceiver which is compliant with astandard selected from the group consisting essentially of licensedradio communications, and unlicensed radio communications operating inthe frequency bands comprising 900 MHz, 5.8 GHz, and 2.4 GHz.
 32. Themethod as recited claim 25 further comprising: determining saidapproximate current location using a position determining system whichis selected from the group consisting essentially of the GlobalPositioning System, the Global Navigation Satellite Service, the GlobalOrbiting Navigation Satellite System, and the Galileo navigation system.